1. Field of the Invention
This invention relates to pneumatic radial tires and more particularly to a pneumatic radical tire having an excellent steering stability and used for passenger cars, this invention increases the rigidity of that portion of the tire which extends from a bead portion to a side portion for the purpose of improving steering stability.
2. Description of the Prior Art
The radial tire has a basic construction comprising a carcass composed of one ply or small number of plies of a layer including cords arranged substantially in parallel with the radial direction of the tire and an inextensible belt layer located at the crown portion of the carcass having a width corresponding to the width of the tread. The radial tire having the above basic construction is suitable for heavy load vehicles such as truck, bus or the like which are used under an inflated condition with a high internal pressure. If such a radial tire is used for passenger cars which are under considerably low pressure when compared with the internal pressure of the radial tire for heavy load vehicles, the inherent property of the carcass that can easily be deformed by the exterior force acting upon various directions of the tire exhibits a comfortable riding feeling in the up and down directions. On the contary, the surplus deformation of the carcass in fore and aft directions and left and right directions tends to delay the steering response, thereby deteriorating the steering stability of the tire.
Many attempts have heretofore been made to eliminate the defects due to the above mentioned surplus deformation of the carcass while maintaining the good riding feeling. That is, various kinds of measures are taken along the lower region of the sidewall of the tire extending from the bead of the tire to the side portion for the purpose of improving the rigidity of the above-mentioned region, but none has led to a satisfactory result. That is, the reinforcement does not show any remarkable effect; a separation failure or the like is induced in or near the reinforcing portion. In a reinforcement construction described in U.S. Pat. No. 3,853,163, the reinforcement is effected by arranging one strip composed of metal cords inclined at an angle of 5.degree. to 15.degree. with respect to the circumferential direction of the tire and located at the lower region of the sidewall extending from the level of the bead wire located at the outside of the tire axial direction of a turn-up portion of the carcass to the upper limit which is 45% of the tire sectional height. Such a reinforcement construction has the advantage that the arrangement direction of the metal cords tends to improve the rigidity of the tire in the circumferential direction thereof without deteriorating the riding feeling property. But, such reinforcement construction has the disadvantage that the reinforcing efficiency is not sufficient even though the rigidity of the cord material is considerably higher than that of the carcass cord material and that of adjacent or peripheral member such as rubber or the like.